Processing facilities and other facilities routinely include tanks for storing liquid materials and other materials. For example, storage tanks are routinely used in tank farm facilities and other storage facilities to store oil or other materials. As another example, oil tankers and other transport vessels routinely include numerous tanks storing oil or other materials.
Often times, it is necessary or desirable to measure the amount of material stored in a tank. This may be useful, for example, during loading of material into the tank or unloading of material from the tank. As particular examples, “custody transfers” and “weights and measures of oil” often require highly accurate measurements from level gauging instruments installed on the roof of a tank. In bulk storage tanks, an error of one millimeter in a level reading can correspond to several cubic meters of volumetric error. This can result in losses of thousands of dollars for one or more parties.
Radar gauges are one type of non-contact level gauge used for the last several decades. Radar gauges typically transmit wireless signals towards a material in a tank and receive wireless signals reflected off the material in the tank. Unfortunately, radar measurements can be affected by multiple reflections inside a tank, such as reflections from the tank's walls, bottom, roof, and obstructions like agitators, ladders, and heat coils. Furthermore, the full capacity of a tank is often used for storage and transfer. For this reason, level measurements typically need to be constantly reliable even as the level of material approaches the bottom or roof of the tank, which can be difficult to achieve with conventional radar gauges.
One approach to solving these problems is to use narrow radar beams with smaller antennas. A smaller antenna can often fit into various nozzles of a tank, eliminating the costs associated with forming large “man-holes” in the tank. Moreover, narrower beams can avoid reflections from other objects in a tank. Therefore, millimeter-wave radars with ultra-wide bandwidths have been proposed. However, the material in a tank can be aggressive (such as highly corrosive), and the pressure inside the tank can be higher than atmospheric pressure. As a result, robust protection of sensitive level gauging equipment, such as millimeter-wave radars, can be very important for achieving high performance and lower cost.